Removal of H2S and CO2 from a hydrocarbon fluid stream

Abstract

A system for removal of Hydrogen Sulfide (H 2 S) and/or Carbon Dioxide (CO 2 ) from natural gas via absorption and disassociation utilizing a sea water contact system. In the preferred embodiment of the present invention, a series of counter current scrubber stages is provided, each configured to remove via absorption/disassociation a portion of the impurities, each stage having less pressure than the predecessor, each stage redirecting the purified gas to the preceding stage, until the contaminant level in the hydrocarbon gas stream has been reduced to an acceptable level. The hydrogen sulfide/carbon dioxide contaminants are thereby sequestered in the sea water utilized in the scrubber, which sea water may be further processed and/or re-introduced into the deep of a body of water, where the contaminants will remain isolated for hundreds of years. The present invention further contemplates and energy recovery system for greatly enhancing the efficiency of the system. Accordingly, the present invention provides an efficient and cost effective method for the purification of natural gas on an offshore platform.

1. The method of removal and isolation of impurities in a gas stream, comprising the steps of:
 a.) flowing said gas stream though a first stage scrubber having an operating pressure, such that said gas stream undergoes counter-current contact with sea water, sequestering a portion of said impurities and a portion of said gas stream in said sea water, so as to provide first stage sequestered sea water, and a purified gas stream;  
 b.) flowing said first stage sequestered sea water through a second stage scrubber having a lesser operating pressure than said first stage scrubber, providing a second stage pressure differential;  
 c.) utilizing said second stage pressure differential to flash impurities and gas sequestered from said first stage sequestered sea water, providing a second stage gas stream;  
 d.) flowing said second stage gas stream though said second stage scrubber, such that said second stage gas stream undergoes counter-current contact with sea water, sequestering a portion of said impurities and a portion of said gas stream in said sea water, so as to provide second stage sequestered sea water, and a second stage purified gas stream.  
 
     
     
       2. The method of  claim 1 , wherein after step “d. there is provided the additional steps of:
 e.) compressing said second stage purified gas, producing heated, compressed gas having a pressure about that of said first stage scrubber;  
 f.) directing said heated, compressed gas into said first stage scrubber, and  
 g.) cooling said heated, compressed gas in said first stage scrubber via heat exchange with said seawater therein.  
 
     
     
       3. The method of  claim 2 , wherein after step “g” there is provided the additional steps of:
 h.) flowing said second stage sequestered sea water through a third stage scrubber having a lesser operating pressure than said second stage scrubber, providing a third stage pressure differential;  
 l.) utilizing said third stage pressure differential to flash impurities and gas sequestered from said second stage sequestered sea water, providing a third stage gas stream;  
 j.) flowing said third stage gas stream though said third stage scrubber, such that said third stage gas stream undergoes counter-current contact with sea water, sequestering a portion of said impurities and a portion of said gas stream in said sea water, so as to provide third stage sequestered sea water, and a third stage purified gas stream.  
 
     
     
       4. The method of  claim 3 , wherein there is provided after step “j.” the additional steps of
 k.) compressing said third stage purified gas stream, producing heated, compressed gas having a pressure about that of said second stage scrubber  
 l.) re-introducing said heated compressed gas into said second stage scrubber; and  
 m.) cooling said heated, compressed gas in said first stage scrubber via heat exchange with said seawater therein.  
 
     
     
       5. The method of  claim 4 , wherein after step “m” there is provided the additional steps of:
 n.) flowing said third stage of sequestered sea water through a fourth stage scrubber having a lesser operating pressure than said second stage scrubber, providing a fourth stage pressure differential;  
 o.) utilizing said fourth stage pressure differential to flash impurities and gas sequestered from said third stage sequestered sea water, providing a fourth stage gas stream;  
 p.) flowing said fourth stage gas stream though said fourth stage scrubber, such that said fourth stage gas stream undergoes counter-current contact with sea water, sequestering a portion of said impurities and a portion of said gas stream in said sea water, so as to provide fourth stage sequestered sea water, and a fourth stage purified gas stream.  
 
     
     
       6. The method of  claim 1 , wherein there is provided after step “d.” the additional steps of:
 d1. placing a first control valve situated between said first stage scrubber and said second stage scrubber so as to allow the passage of said first stage sequestered sea water from said first stage scrubber therethrough so as to facilitate a. drop in pressure of said first stage sequestered seawater flowing to said second stage scrubber, so as to provide said first stage pressure differential;  
 d2. utilizing a first energy recovery turbine to extract energy from first stage pressure differential; providing first stage extracted energy;  
 d3. utilizing said first stage extracted energy to power a pump for pumping seawater into said second stage scrubber.  
 
     
     
       7. The method of  claim 3 , wherein there is provided after step “p” the additional steps of:
 p1. placing a second control valve situated between said second stage scrubber and said third stage scrubber so as to allow the passage of said second stage sequestered sea water from said second stage scrubber therethrough, so as to facilitate a drop in pressure of said second stage sequestered sea water flowing to said third stage scrubber, so as to provide a second stage pressure differential;  
 p2. utilizing a second energy recovery turbine to extract energy from said second stage pressure differential; providing second stage extracted energy;  
 p3. utilizing said second stage extracted energy to power a pump for pumping seawater into said second stage scrubber.  
 
     
     
       8. The method of  claim 2 , wherein after step “g.” there is provided the further step “g1.” of pumping said second stage sequestered sea water to a depth of at least 100 feet in a body of water. 
     
     
       9. The method of removing a contaminant from natural gas, comprising the steps of:
 a.) flowing said natural gas though a first stage scrubber having an operating pressure above atmospheric pressure;  
 b) subjecting said natural gas to counter-current contact with a flow of seawater;  
 c) sequestering said contaminant and a portion of said natural gas in said seawater, so as to provide first stage sequestered seawater;  
 d.) flowing said first stage sequestered sea water through a second stage scrubber having a lesser operating pressure than said first stage scrubber, providing a second stage pressure differential;  
 e.) utilizing said second stage pressure differential to flash natural gas from said first stage sequestered seawater, providing a second stage gas stream;  
 f.) flowing said second stage gas stream though said second stage scrubber, such that said second stage gas stream undergoes counter-current contact with sea water, sequestering said contaminant in said second stage gas stream in said sea water, so as to provide second stage sequestered sea water, and a second stage purified gas stream.  
 
     
     
       10. The method of  claim 9 , wherein after step “f.” there is provided the additional steps of:
 g.) compressing said second stage purified gas producing heated, compressed gas having a pressure about that of said first stage scrubber;  
 h.) directing said heated, compressed gas into said first stage scrubber, and  
 i.) cooling said heated, compressed gas in said first stage scrubber via heat exchange with said seawater therein.  
 
     
     
       11. The method of removing a contaminant from natural gas, comprising the steps of:
 a.) sequestering a portion of said natural gas and said contaminant into H 2 O, providing sequestered liquid;  
 b.) subjecting said sequestered liquid to a reduced atmospheric pressure to facilitate the migration of said natural gas from said H 2 O, while retaining a portion of said contaminant in said H 2 O, so as to provide purified natural gas and contaminant infused H 2 O;  
 c.) collecting said purified gas,  
 d.) repeating steps a through c, until said natural gas is processed to the desired purity.  
 
     
     
       12. The method of removing a contaminant from a gas stream, comprising the steps of:
 a.) sequestering a portion of said gas stream and said contaminant into a liquid;  
 b.) subjecting said liquid to a reduced atmospheric pressure to facilitate the migration of said gas stream from said liquid, while retaining a portion of said contaminant in said liquid, so as to provide a purified gas stream;  
 c.) collecting said purified gas stream, and  
 d.) repeating steps a through c, until said gas stream is processed to the desired purity.  
 
     
     
       13. The method of  claim 12 , wherein said gas stream comprises exhaust gas. 
     
     
       14. The method of  claim 13 , wherein said exhaust gas comprises flue gas. 
     
     
       15. The method of  claim 14 , wherein said contaminant comprises H 2 S. 
     
     
       16. The method of  claim 15 , wherein said contaminant comprises CO 2 . 
     
     
       17. The method of  claim 12 , wherein said gas stream comprises hydrocarbon gas. 
     
     
       18. The method of  claim 17 , wherein said gas stream comprises natural gas. 
     
     
       19. The method of  claim 18 , wherein said contaminant comprises H 2 S. 
     
     
       20. The method of  claim 19 , wherein said contaminant comprises CO 2 . 
     
     
       21. The method of  claim 20 , wherein said liquid comprises seawater. 
     
     
       22. The method of  claim 21 , wherein after step “d.” there further comprises the additional step “e.” of pumping said liquid and contaminant into a body of water to a depth of over 100 feet.